1. 2012

    Color Glass Condensate

    Over the past few days, the news about the LHC possibly discovering (or even confirming, in some sources!) a new kind of matter has popped up on quite a few websites — blogs, science news sites, Twitter, Google+, Reddit, elsewhere on Reddit, you name it. Of course, I was writing about this before it was cool :-) I reported the discovery of the ridge presented by CMS at the High pT LHC Physics Workshop. Back then it wasn’t clear that anyone really knew what was going on, but of course that important fact got lost in the hype.

    As I posted in a more recent update, there is a lot of speculation that this ridge might have something to do with something called the color glass condensate (CGC). This is what so many sites are calling the new state of matter that the LHC has supposedly discovered. Well, I actually know something about this! Sort of. The CGC is an incredibly complex mathematical model, but it is somewhat closely related to what I work on, so I figured I could try to explain what’s going on in some more detail.

    Parton distributions

    All this starts with the question: what’s …

  2. 2012

    New type of matter?

    Phys.org has picked up on the results from the LHC pilot pA run showing the formation of The Ridge in high-multiplicity collisions. I wrote about this last month, when it was first presented at the High-pT LHC Physics Workshop in Wuhan, and at that time, the sentiment at the conference seemed to be that it wasn’t clear what could be causing the ridge.

    Now, people are starting to lean toward the color glass condensate (CGC) as an explanation. The CGC has been called a new state of matter, which probably isn’t the worst description, but I think that makes it sound like more than it is. It’s a model that predicts the behavior of gluons within a proton or nucleus, under conditions in which the gluons are so numerous that they regularly “bump into” each other and fuse, or “recombine” to use the technical term. (That’s an extreme oversimplification, of course; perhaps someday I’ll do a post explaining this in more detail.) This model predicts some correlations among gluons which might be able to explain the ridge. But it’s not at all clear yet that that is the case. The LHC didn’t …

  3. 2012

    Results from HPT 2012

    One unexpected perk of being in China: I woke up before 7:30 this morning. That would never happen without jet lag.

    Unfortunately, even waking up at 7:30 every day hasn’t given me any time to write up a mid-conference blog post. Talks have been running from 8:30-6:30, with the rest of the time mostly taken up by meals and discussions. So I’ll just post this “teaser” of some of the more interesting results that were presented.

    Of the presentations that gave new results, most of them are based the September proton-lead run at the LHC. This was just a pilot run, meant to ensure that there wouldn’t be any unexpected problems with colliding two different types of particles, so there wasn’t a lot of data collected — only 2 million collisions — but it was already enough to start shedding some light on the underlying physics.

    No initial state effects

    Ion-ion collisions have already been extensively studied at both RHIC and the LHC, and as you might imagine, when you smash a blob of a hundred blobs of particles into another blob of a hundred blobs of particles, what you get is a mess …